# Detecting space time

1. Mar 1, 2006

### wolram

It is just a thought, but how can space time be detected? i guess gravitational radiation is one way, is this the only way?

2. Mar 1, 2006

### Perturbation

Detected? It's not really like a tangible thing. I guess if you wanted to have experiment supporting the notion of space-time, you'd just have to look to those verifying special and general relativity or relativistic quantum mechanics etc.

3. Mar 1, 2006

### AlphaNumeric

Almost by definition, if something happen somewhere, then that 'somewhere' belongs to spacetime.

4. Mar 2, 2006

### bernhard.rothenstein

If you think about the space time coordinates of a distant event you could use the radar or photographic detection.

5. Mar 2, 2006

### Ich

AFAIK Gauss was the first to examine the properties of space. When working as a geodesist he checked the sum of angles of large triangles (~100 km). Of course he found no significant deviation from 180°.

6. Mar 2, 2006

### HallsofIvy

It's not at all clear what you mean by "detect space-time". Ich assumed you meant "detect the curvature of space-time" which is probably the best interpretation. As he said, Gauss attempted to determine if space is Euclidean by measuring the angles in a triangle formed by 3 mountain peaks using the best surveying equipment. He found any deviation from 180 degrees to be less than the error of measurement.

One difficulty with that is defining how you are going to measure things. Imagine using, say, Pluto, Uranus, and Neptune, at times when they are farthest apart in their orbits, as vertices of a triangle and thin steel bars as straight edges! Since, in relativity, there are no perfectly rigid materials, those bars would "sag" inward toward the sun- you would find the angles to be less than 180 degrees- elliptic geometry- and dependent upon the rigidity of the materials.

It would make much more sense to use laser beams as straight lines. Since it has been experimentally verified that light beams bend as they pass a star (the sun), your lines would appear curved and you would find the sum of the angles to be greater than 180 degrees- hyperbolic geometry- and that the curvature changed from moment to moment as the masses in the system moved.